I have hundreds of BC547 general purpose transistors. Will this work in the
place of a 2N4401 BJT?

----- Original Message -----
From: "Spehro Pefhany" <speff@interlog.com>
To: "Microcontroller discussion list - Public." <piclist@mit.edu>
Sent: Tuesday, May 31, 2005 2:35 PM
Subject: Re: [PIC] Pin Protection


> At 11:29 AM 5/31/2005 +0200, you wrote:
> >Dear Spehro Pefhany,
> >
> >Thanks, I have looked at your circuit. Just want to clear up some
confusion.
> >
> >According to the schematic there are a ground(0V track on the PCB) and a
> >earth(close to the spark gap).
>
> Yes, they are connected together, close to the where the fence loop return
> connects.
>
> >The transistor, 10K Resister, 10uF cap and TVS are all connected to the
> >ground.
>
> Yes.
>
> >There must also be a short(thick) track from the TVS to the pad that will
> >connect the ground to earth
> >Do I understand this correctly?
>
> Correct.
>
>
> >So when the loop is fine there will be a approx 1mA current and the PIC
> >input will be low.
>
> High.
>
> >When the loop gets broken there will be approx 0.23mA
> >current. The Transistor base will see approx 2.3V
>
> 0.6V, because it's a BJT with ~250uA flowing into the base
>
> >  and the PIC input will
> >read High
>
> Low.
>
> Best regards,
>
> Spehro Pefhany --"it's the network..."            "The Journey is the
reward"
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>
>
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